Internal combustion engine can include a pilot subchamber in which a pilot portion of the fuel is injected and ignited before being directed into the main combustion chamber, where further fuel is injected to complete the combustion.
Some internal combustion engines have relatively large pilot subchambers and pilot injectors, thus providing a relatively large portion of the fuel flow as a pilot injection. Accordingly, a relatively large pilot fuel flow is injected, which creates a relatively rich overall fuel mixture in the combustion chamber in conditions where the engine operates solely on pilot injection flow.